In situ measurements of calcium carbonate dissolution under rising CO2 pressure using underwater laser-induced breakdown spectroscopy. Issue 7 (1st June 2016) - Goueguel, Christian L.
Abstract : Underwater laser-induced breakdown spectroscopy was applied for rapid in situ measurements of CaCO3 dissolution in CO2 -saturated water at high pressure. Abstract : In the present study, we applied underwater laser-induced breakdown spectroscopy (underwater LIBS) for rapid in situ measurements of calcium carbonate (CaCO3 ) dissolution as a function of CO2 pressure ( p CO2 ). A pulsed Nd:YAG laser at 1064 nm was used to produce gaseous plasma in the fluid surrounding a pressed pellet of CaCO3 powder. The ensuing plasma emission was spectrally analyzed, and the intensity of the calcium emission line at 422.67 nm was used to monitor Ca 2+ cation released to the water. Barium emission line at 455.40 nm was simultaneously recorded as an internal standard to calibrate calcium signal intensity. The study shows that relatively strong and well-resolved spectral lines of both Ca 2+ and Ba 2+ cations can be obtained in CO2 -saturated water. More importantly, the results show that underwater LIBS is capable of performing quantitative analysis at elevated p CO2, with an estimated Ca 2+ detection limit of about 9 ppm over 50–350 bar. In the solution with the initially added CaCO3 pellet, the concentration of Ca 2+ increases by a factor of 2 as p CO2 increases from 50 to 150 bar and remains nearly constant when p CO2 is further increased up to 350 bar. Finally, our study provides evidence that underwater LIBS could be a useful tool to investigate/monitor carbonate dissolution (at low ppm levels) in various geochemical applications.